The purpose of this project is to identify and study populations with altered immunologic states experiencing unusual rates of malignancy. Risks of cancer of different sites are quantified for various groups of such patients, compared with each other, and characteristics and possible determinants of unusual risks are sought. The populations studied include renal transplant recipients, patients with inherited and acquired immune deficiency syndromes, and groups of immunostimulated persons. Both cohort studies of these groups of patients and case-control studies of such patients who also developed cancer are being conducted.